In one known form of locking device of the above kind, the plug has a key-receiving slot for a double-entry edge-profiled key, the tumblers being arranged in two separate banks respectively positioned at opposite sides of the slot, the tumblers in the two banks operating independently and thereby providing the same security as an equal number of tumblers arranged in a single row extending axially of the plug in the usual manner, the edge profile of the key being common to both banks of tumblers.
The internal configuration of the body of the plug of the known locking device is of complex form, including a separate slot to receive each tumbler together with further separate slots each to receive a spring acting on the associated tumbler to urge it into its projecting position, each spring being disposed between a projection on the associated plunger and a staking bar.
With the present requirements for automatic assembly operations to reduce manufacturing costs, there is a demand for greater precision and a reduction of tolerance levels. These have not been achieved with the present methods of production in which the plug has been formed as a one-piece zinc-based die-casting, despite the use of complex and expensive tooling constructions. It is accordingly an object of the invention to provide an improved form of a plug for a locking device of the kind specified.